A considerable amount of experience has been accumulated in converting compact research reactors from highly-enriched uranium (HEU) to low-enriched uranium (LEU). Although the details of naval-reactor design are closely held military secrets, during the Gorbachev period, the Soviet Union supplied the Norwegian government with some basic data, including the dimensions and 235U content of the core of the HEU fueled KLT-40 reactor used in some Russian nuclear-powered icebreakers. A group of Norwegian analysts used this information to develop a simple model of the KLT-40 core. We have calculated the neutronics behaviors of variants of these core models as a function of 235U burnup and conclude that the reactors could be fueled with LEU without loss of core life. We also show that simplified infinite-core calculations can be used for such studies.